Local surface measurements of rubrene single crystals reveal interesting insights on carrier transport mechanisms at the active interface of high-performance field-effect "air-gap stamp" transistors. Scanning tunnelling microscopy (STM) images, combined with atomic force microscopy and X-ray diffraction, reveal directly the position and orientation of individual molecules in the a-b plane (see figure and inside cover). Local current-voltage curves recorded using STM in the dark and under light indicate a rectifying p-type behavior.